The insulin-like growth factors, also known as somatomedins, include insulin-like growth factor-I (IGF-I) and insulin-like growth factor-II (IGF-II) (Klapper, et al., (1983) Endocrinol. 112:2215 and Rinderknecht, et al., (1978) Febs. Lett. 89:283). These growth factors exert mitogenic activity on various cell types, including tumor cells (Macaulay, (1992) Br. J. Cancer 65:311), by binding to a common receptor named the insulin-like growth factor receptor-1 (IGF1R) (Sepp-Lorenzino, (1998) Breast Cancer Research and Treatment 47:235). Interaction of IGFs with IGF1R activates the receptor by triggering autophosphorylation of the receptor on tyrosine residues (Butler, et al., (1998) Comparative Biochemistry and Physiology 121:19). Once activated, IGF1R, in turn, phosphorylates intracellular targets to activate cellular signaling pathways. This receptor activation is critical for stimulation of tumor cell growth and survival. Therefore, inhibition of IGF1R activity represents a valuable potential method to treat or prevent growth of human cancers and other proliferative diseases.
Several lines of evidence indicate that IGF-I, IGF-II and their receptor IGF1R are important mediators of the malignant phenotype. Plasma levels of IGF-I have been found to be the strongest predictor of prostate cancer risk (Chan, et al., (1998) Science 279:563) and similar epidemiological studies strongly link plasma IGF-I levels with breast, colon and lung cancer risk.
Overexpression of Insulin-like Growth Factor Receptor-1 has also been demonstrated in several cancer cell lines and tumor tissues. IGF1R is overexpressed in 40% of all breast cancer cell lines (Pandini, et al., (1999) Cancer Res. 5:1935) and in 15% of lung cancer cell lines. In breast cancer tumor tissue, IGF1R is overexpressed 6-14 fold and IGF1R exhibits 2-4 fold higher kinase activity as compared to normal tissue (Webster, et al., (1996) Cancer Res. 56:2781 and Pekonen, et al., (1998) Cancer Res. 48:1343). Ninety percent of colorectal cancer tissue biopsies exhibit elevated IGF1R levels wherein the extent of IGF1R expression is correlated with the severity of the disease. Analysis of primary cervical cancer cell cultures and cervical cancer cell lines revealed 3- and 5-fold overexpression of IGF1R, respectively, as compared to normal ectocervical cells (Steller, et al., (1996) Cancer Res. 56:1762). Expression of IGF1R in synovial sarcoma cells also correlated with an aggressive phenotype (i.e., metastasis and high rate of proliferation; Xie, et al., (1999) Cancer Res. 59:3588). Furthermore, acromegaly, a slowly developing disease, is caused by hypersecretion of growth hormone and IGF-I (Ben-Schlomo, et al., (2001) Endocrin. Metab. Clin. North. Am. 30:565-583). Antagonism of IGF1R function may be helpful in treating the disease. There remains a need in the art for IGF1R antagonist therapies for treating or preventing such disease and disorders. Of particular utility are anti-IGF1R antibody based therapies.